Engine Mechanical problem
1991 Lexus LS 400 V8 Two Wheel Drive Automatic 187000 miles

I called the repair shop and explained what my car was doing before it stop running. And, when I had my car towed to the repair shop, again I explained how my car had been running before I had to just park it: 1.) I would be driving and my car RMPs would surge suddenly; 2.) The car would travel speeds around 15-20 mph, like it was not getting any gas just idled; 3.) Finally, the car would start up, but died went put into Reverse and/or Drive. Yhe mechanin replaced water pump and fixed the Timing Belt ($900.) The car again started having same problem and after 50 mi the car can not be driven. Now, I am told its the "Idle Control Sensor." Repair shop DID NOT run a diagnostics test. I am refusing to pay any more monies--Shop was paid to fix car and failed to. Please advise. JERI